How to tile/repeat gradient texture based on object polygons faces, in shader editor?
One way to make that is by creating a special UV unwraping which will basically take every face of your model and unwrap them all on top of each other and taking the entire UV space.

If you have other UV maps already, make sure to first create a new UV map in your object so you don't lose your previous UV maps:



Then select the new UV Map, go to edit mode, select everything with A then press U → Reset. This will result to something like this in your UV Editor:



Once you've got that, you will need to call that specific UV map in your shader. Go to the shader editor, hit &#8679; ShiftA → Input → UV Map. Specify the UV Map you want in that node, then do whatever you want with that: